The Oxidative Stress Mechanisms Of HORMESIS Induced By Low-dose Cadmium And Phenanthrene

Hormesis, which is attracting more and more attention, has become a challenge to toxicology traditional model. In the present study, The mortality of earthworm Eisenia foetida, the activities of catalase (CAT), superoxide dismutase (SOD), Glutathione peroxidase (GSH-PX), endocytic and the content of H2O2 and malondialdehyde(MDA) were determinated in the different concentrations of cadmium and phenathrene. Also, the models of hormesis induced by cadmium and phenanthrene in soil environment were established by using the best non-linear curve fitting techniques and flow cytometer method. Therefore, the oxidative stress mechanisms of homesis induced by low-dose cadmium and phenanthrene were elucidated. These results provided a scientific basis to reveal some molecular mechanisms of hormestic effect and further understand the hormesis caused by chemicals. The main findings are as follows:1. Cadmium alone and combination with phenanthrene at low concentration might induce the hormesis which is characterized by an inverted U-shaped dose response.. The results from the survival and weight of earthworm showed that low dose cadmium alone or cadmium plus 4mg/kg phenanthrene induced a stimulation, but high concentrations inhibition after exposure of 7th and 17th day, expectively..2. The horemtic effect of CAT activity was found in the earthworms exposed to soil with low dose cadmium and phenenathrene. This effect was charactered by significant time-dependent effect. The hormetic magnitudes of CAT induced by combined pollution were stronger than those induced by cadmium alone. In filter paper pollution experiment, the hormestic model for cadmium was Y=-31.576+16.901X -1.206X 2. The hormetic magnitude was 36.8%, and the maximum hormetic effect was 27.637%. The soil pollution experiment showed the hormesis model after 7 days of exposure was Y = - 0.7669+ 0.4792X -0.0535X2. However, after 14 days of exposure, the hormesis was disappeared and the activity of CAT was decreasing as the concentration becomes higher, the model was Y = - 0.2243-0.1068X.3. The hormetic effect of GSH-PX activity which induced by cadmium single pollution or combined pollution between cadmium and phenenathrene became lower as the time longer. The maximum hormetic effects after exposure of 7 and 14 days in low-dose cadmium soil pollution were 122.58% and 28.04%, respectively. The hormetic model of 7 day for single cadmium pollution was Y=-115.407+0.702X-0.0005X2, and the magnitude of hormetic effect was 174.75%.4. The hormesis models of GSH-PX activity which induced by cadmium single exposed on the filter paper or in the soil environment were Y=-20.521+1?7.876X-0.452X2 and Y=-135.16+0.6112X-0.0003X2, respectively. After 4h filter paper exposure, the hormetic effect was 52.8% and the maximium hormesis was 34.498%.5. The content of H2O2 in earthworm coelomocyte was characterized by J shaped hormetic effect. As the concentration of cadmium becomes higher, the content of H2O2 was increasing then decreasing. The hormetic effect model was Y =–1295.5- 560.78X+27.977X26. The content of MDA in earthworm increase at low dose of combined pollution with cadmium and phenanthrene, but high does decreased. It was also characterized by J shaped hormetic effect which means beneficial to the organism at low dose and harmful at high dose.7. There was a significant hormetic effect of phagocytosis which indued by the single cadmium pollution. The low dose cadmium can induce the phagocytosis activity of phagocytosis cell. As the concentration becomes higher, the H2O2 which produced by cell respiration leads an oxidative stress, the oxidizing of cell lipid, the increasing of MDA, and the oxidative damage of cell in the earthworm with increasing cadmium concentration.